RTCRtpStreamStats.qpSum

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qpSum 特性为 RTCRtpStreamStats dictionary is a value generated by adding the Quantization Parameter ( QP ) values for every frame sent or received to date on the video track corresponding to this RTCRtpStreamStats 对象。 In general, the higher this number is, the more heavily compressed the video data is.

句法

var qpSum = RTCRtpStreamStats.qpSum;

值

An unsigned 64-bit integer value which indicates the sum of the quantization parameter (QP) value for every frame sent or received so far on the track described by the RTCRtpStreamStats object. Since the value of QP is typically larger to indicate higher compression factors, the larger this sum is, the more heavily compressed the stream generally has been.

注意： This value is only available for video media.

用法注意事项

Quantization is the process of applying lossy compression to a range of values, resulting in a single quantum value . This value takes the place of the range of values, thereby reducing the number of different values that appear in the overall data set, making the data more compressible. The quantization process and the amount of compression can be controlled using one or more parameters.

It's important to keep in mind that the value of QP can change periodically—even every frame—so it's difficult to know for certain how substantial the compression is. The best you can do is make an estimate. You can, for example, use the value of RTCReceivedRtpStreamStats.framesDecoded if receiving the media or RTCSentRtpStreamStats.framesEncoded if sending it to get the number of frames handled so far, and compute an average from there. See Calculating average quantization below for a function that does this.

Also, the exact meaning of the QP value depends on the codec being used. For example, for the VP8 codec, the QP value can be anywhere from 1 to 127 and is found in the frame header element "y_ac_qi" , whose value is defined in RFC 6386: 19.2 . H.264 uses a QP which ranges from 0 to 51; in this case, it's an index used to derive a scaling matrix used during the quantization process. Additionally, QP is not likely to be the only parameter the codec uses to adjust the compression. See the individual codec specifications for details.

范例

Calculating average quantization

calculateAverageQP() function shown below computes the average QP for the given RTCRtpStreamStats object, returning 0 if the object doesn't describe an RTP stream.

function calculateAverageQP(stats) {
  let frameCount = 0;
  switch(stats.type) {
    case "inbound-rtp":
    case "remote-inbound-rtp":
      frameCount = stats.framesDecoded;
      break;
    case "outbound-rtp":
    case "remote-outbound-rtp":
      frameCount = stats.framesEncoded;
      break;
    默认：
      return 0;
  }
  return status.qpSum / frameCount;
}

规范

规范	状态	注释
Identifiers for WebRTC's Statistics API The definition of 'RTCInboundRtpStreamStats: qpSum' in that specification.	候选推荐	初始定义。
Identifiers for WebRTC's Statistics API The definition of 'RTCOutboundRtpStreamStats: qpSum' in that specification.	候选推荐	初始定义。

浏览器兼容性

The compatibility table on this page is generated from structured data. If you'd like to contribute to the data, please check out https://github.com/mdn/browser-compat-data and send us a pull request. 更新 GitHub 上的兼容性数据

	桌面						移动
	Chrome	Edge	Firefox	Internet Explorer	Opera	Safari	Android webview	Chrome for Android	Firefox for Android	Opera for Android	Safari on iOS	Samsung Internet
`qpSum`	Chrome No	Edge No	Firefox 66	IE No	Opera No	Safari ?	WebView Android No	Chrome Android No	Firefox Android 66	Opera Android No	Safari iOS ?	Samsung Internet Android No

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元数据

最后修改： Jan 26, 2020

WebRTC API
RTCRtpStreamStats
特性
1. codecId
2. firCount
3. kind
4. nackCount
5. pliCount
6. qpSum
7. sliCount
8. ssrc
9. trackId
10. transportId
Related pages for WebRTC

在此页

句法

值

用法注意事项

范例

Calculating average quantization

规范

浏览器兼容性

图例

相关话题